1. Field of the Invention
The present invention relates to a golf ball, and more particularly, to the golf ball having no difference in its flight performance irrespective of the position of the rotational axis thereof. To this end, the aerodynamic symmetrical property of the golf ball is improved by providing a novel arrangement of great circles not intersecting dimples arranged according to a regular octahedron and volumes of dimples according to zones of the golf ball.
2. Description of the Related Arts
Normally, 300 to 550 dimples are formed on the surface of a golf ball to improve the aerodynamic characteristic thereof and as such increase the flight distance thereof. Of various proposals which have been hitherto made to improve the dimple arrangement of the golf ball, regular octahedral dimple arrangement has been most widely adopted because the regular dimple octahedral arrangement is orderly in design and favorable in symmetrical property.
As shown in FIG. 8, according to the regular octahedral dimple arrangement, the spherical surface of a golf ball 1 is divided into eight spherical triangles by projecting ridge lines 2a of an octahedron 2 which inscribes the golf ball 1 on the spherical surface of the golf ball 1, then dimples are arranged equivalently inside each spherical triangle. The lines corresponding to the ridge lines 2a projected on the spherical surface of the golf ball 1 form three great circles 3, 4, and 5 not intersecting dimples. One of the great circles 3, 4, and 5, for example, the great circle 3 intersects at right angles with the other great circles 4 and 5 each at two points 4a, 4b, and 5a, 5b.
Normally, the golf ball is molded by a pair of upper and lower semispherical molds. Therefore, dimples cannot be arranged on the parting line on which the upper and lower molds contact with each other. For example, in the golf ball 1 having regular octahedral dimple arrangement, one of the three great circles 3, 4, and 5 is on the parting line which is called the seam. According to the regular octahedral dimple arrangement, since no dimples are arranged on the other two great circles, these two great circles are equivalent to the seam. Therefore, they are called semi-seam. Assuming that the great circle 3 is the seam as shown in FIG. 9, the great circles 4 and 5 are semi-seams. That is, according to the regular octahedral dimple arrangement, the golf ball 1 has one seam 3 and two semi-seams 4 and 5.
The golf ball flies with backspin when it is hit by a golf club. Preferably, the golf ball has no difference in trajectory height and flight distance even though the rotational axis of the backspin is different. If the flight performance of the golf ball is varied due to a different hitting point, namely, the shift of a rotational axis, the golf ball cannot display a player's ability faithfully.
The method for hitting the golf ball having the regular octahedral dimple arrangement is divided into the following three kinds owing to the shift of the rotational axis of the backspin caused by a varied hitting position:
Seam hitting: The golf ball 1 is hit such that a circumference which rotates fastest in its backspin concides with the seam 3.
Semi-seam hitting: The golf ball 1 is hit such that the circumference which rotates fastest in its backspin concides with the semi-seam 4 or 5.
Non-seam hitting: The golf ball 1 is hit such that a circumference which rotates fastest in its backspin doesn't concide with the seam 3, the semi-seam 4 and 5.
In the golf ball 1 having the regular dimple octahedral arrangement, the trajectory height thereof in seam-hitting and semi-seam hitting is lower than in non-seam hitting, and the duration of flight in seam-hitting and semi-seam hitting is shorter than in non-seam hitting. This is because a great circle having no dimples arranged on the circumference which rotates fastest in its backspin and consequently, the dimple effect of the golf ball in seam-hitting and semi-seam hitting is not displayed as favorably as in non-seam hitting. Since the dimple arrangement in seam hitting and in semi-seam hitting is equivalent to each other, the dimple effect of both hittings is similar. Therefore, the trajectory height and duration of flight in semi-seam hitting and seam hitting are similar to each other.
As apparent from the foregoing description, in the golf ball having regular octahedral dimple arrangement, it has a difference in the flight distance and aerodynamic symmetrical property among non-seam hitting, seam hitting, and semi-seam hitting.
In order to improve the aerodynamic characteristic which is deteriorated owing to the difference in the hitting position of the golf ball caused by the seam on which dimples are not formed, the present applicant proposed a dimple arrangement in Japanese Patent Laid-Open Publication No. 61-284264. According to this dimple arrangement, the volumes of dimples positioned in the vicinity of the seam are greater than those of dimples positioned in the vicinity of the poles.
Applying this dimple arrangement to the golf ball having regular octahedral dimple arrangement, in seam hitting, dimples positioned in the vicinity of the circumference which rotates fastest in its backspin have all great volumes. Consequently, the golf ball has an improved dimple effect, thus having a trajectory similar to that in non-seam hitting.
However, in the golf ball in which the volumes of dimples positioned in the vicinity of the seam are greater than those of dimples positioned in the vicinity of the poles, the trajectory in semi-seam hitting is lower than that in non-seam hitting and the duration of flight is shorter in semi-seam hitting than that in non-seam hitting. This is because in semi-seam hitting, all dimples positioned in the vicinity of a circumference which rotates fastest in its backspin do not have greater volume, but both dimples of the greater volumes and smaller volumes are arranged there.